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(gmp.info)Random State Seeding

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Random State Seeding
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 - Function: void gmp_randseed (gmp_randstate_t STATE, mpz_t SEED)
 - Function: void gmp_randseed_ui (gmp_randstate_t STATE,
          unsigned long int SEED)
     Set an initial seed value into STATE.

     The size of a seed determines how many different sequences of
     random numbers that it's possible to generate.  The "quality" of
     the seed is the randomness of a given seed compared to the
     previous seed used, and this affects the randomness of separate
     number sequences.  The method for choosing a seed is critical if
     the generated numbers are to be used for important applications,
     such as generating cryptographic keys.

     Traditionally the system time has been used to seed, but care
     needs to be taken with this.  If an application seeds often and
     the resolution of the system clock is low, then the same sequence
     of numbers might be repeated.  Also, the system time is quite easy
     to guess, so if unpredictability is required then it should
     definitely not be the only source for the seed value.  On some
     systems there's a special device `/dev/random' which provides
     random data better suited for use as a seed.